Method and apparatus for transceiving a MIMO packet in a wireless LAN system

ABSTRACT

A method of transmitting a multiple input multiple output (MIMO) packet by a transmitter in a wireless local area network (WLAN) system is provided. The method includes: generating a MIMO packet including at least one spatial stream set transmitted respectively to at least one receiver, wherein each spatial stream set is encoded on the basis of one of two encoding schemes; transmitting first control information including a MIMO indicator and a first modulation and coding scheme (MCS) field, wherein the MIMO indicator indicates whether the MIMO packet is for single user (SU)-MIMO or multi user (MU)-MIMO, and the first MCS field indicates an MCS used for the MIMO packet if the MIMO packet is for SU-MIMO transmission, and indicates an encoding scheme applied for each of the spatial stream sets if the MIMO packet is for MU-MIMO transmission; and transmitting the MIMO packet to at least one receiver.

This application is the National Phase of PCT/KR2011/004819 filed onJun. 30, 2011 which claims priority under 35 U.S.C. 119(e) to U.S.Provisional Application Nos. 61/360,915 filed on Jul. 1, 2010,61/362,673 filed on Jul. 8, 2010, and 61/407,546 filed on Oct. 28, 2010,all of which are hereby expressly incorporated by reference into thepresent application.

TECHNICAL FIELD

The present invention relates to a wireless local area network (WLAN)system, and more particularly, to a method of transmitting and receivinga packet on the basis of a multiple input multiple output (MIMO)transmission scheme by an access point (AP) and a station (STA).

BACKGROUND ART

With the advancement of information communication technologies, variouswireless communication technologies have recently been developed. Amongthe wireless communication technologies, a wireless local area network(WLAN) is a technology whereby Internet access is possible in a wirelessfashion in homes or businesses or in a region providing a specificservice by using a portable terminal such as a personal digitalassistant (PDA), a laptop computer, a portable multimedia player (PMP),etc.

The IEEE 802.11n is a technical standard relatively recently introducedto overcome a limited data rate which has been considered as a drawbackin the WLAN. The IEEE 802.11n is devised to increase network speed andreliability and to extend an operational distance of a wireless network.More specifically, the IEEE 802.11n supports a high throughput (HT),i.e., a data processing rate of up to above 540 Mbps, and is based on amultiple input and multiple output (MIMO) technique which uses multipleantennas in both a transmitter and a receiver to minimize a transmissionerror and to optimize a data rate.

With the widespread use of the WLAN and the diversification ofapplications using the WLAN, there is a recent demand for a new WLANsystem to support a higher throughput than a data processing ratesupported by the IEEE 802.11n. A next-generation WLAN system supportinga very high throughput (VHT) is a next version of the IEEE 802.11n WLANsystem, and is one of IEEE 802.11 WLAN systems which have recently beenproposed to support a data processing rate of above 1 Gbps in a MACservice access point (SAP).

To effectively utilize a radio channel, the next-generation WLAN systemsupports multi user-multiple input multiple output (MU-MIMO)transmission in which a plurality of non-access point (AP) stations(STAs) concurrently access to a channel. According to the MU-MIMOtransmission, an AP can transmit a frame concurrently to one or moreMIMO-paired STAs.

As an encoding scheme, binary convolutional coding (BCC) and low densityparity check (LDPC) encoding are provided in a WLAN system. Since datatransmission and reception between an AP and an STA have a one-to-onerelation in a legacy WLAN system and a WLAN system supporting a highthroughput, it has been enough to attach information related to anencoding scheme of encoded data to a packet to be transmitted. However,a next generation WLAN system may have a different encoding scheme of adata sequence to be transmitted to each STA since the AP can transmitpackets simultaneously to a plurality of STAs by using a MU-MIMOtransmission scheme.

The AP may have a different a modulation and coding scheme (MCS) to besignaled according to a situation where SU-MIMO transmission is achievedto a specific STA or a situation where MU-MIMO transmission is achievedto a plurality of STAs. In case of the SU-MIMO transmission, an MCSindex is signaled to a specific STA. However, in case of the MU-MIMOtransmission, respective MCS indices need to be signaled to a pluralityof MU-MIMO paired STAs. Therefore, there is a need for a method oftransmitting and receiving a packet by considering a MIMO transmissionscheme of an AP and a capability of a transmission target STA in a nextgeneration WLAN system.

SUMMARY OF INVENTION Technical Problem

The present invention provides a method of transmitting and receiving amultiple input multiple output (MIMO) packet in a wireless local areanetwork (WLAN) system supporting a multi user (MU)-MIMO transmissionscheme.

Technical Solution

In an aspect, a method of transmitting a multiple input multiple output(MIMO) packet by a transmitter in a wireless local area network (WLAN)system is provided. The method includes: generating a MIMO packetincluding at least one spatial stream set transmitted respectively to atleast one receiver, wherein each spatial stream set is encoded on thebasis of one of two encoding schemes; transmitting first controlinformation including a MIMO indicator and a first modulation and codingscheme (MCS) field, wherein the MIMO indicator indicates whether theMIMO packet is for single user (SU)-MIMO or multi user (MU)-MIMO, andthe first MCS field indicates an MCS used for the MIMO packet if theMIMO packet is for SU-MIMO transmission, and indicates an encodingscheme applied for each of the spatial stream sets if the MIMO packet isfor MU-MIMO transmission; and transmitting the MIMO packet to at leastone receiver. The two encoding schemes are low-density parity check(LDPC) encoding scheme and binary convolution coding (BCC) encoding.

If the MIMO packet is for MU-MIMO transmission, the MIMO indicator mayindicate MU-MIMO transmission by indicating a receiver group includingthe at least one receiver.

The method may further include transmitting second control informationincluding a second MCS field, wherein the second MCS field indicates anMCS used for each of the at least one spatial stream set if the MIMOpacket is for MU-MIMO transmission.

The method may further include, after transmitting the first controlinformation, transmitting a training sequence used to estimate a MIMOchannel between the transmitter and the at least one receiver beforetransmitting the second control information.

The first control information may further include ‘the number of spatialstream’ sub-field indicating the number of spatial streams included ineach of the at least one spatial stream.

In another aspect a wireless apparatus is provided. The apparatusincludes: a transceiver for receiving or transmitting a MIMO packet; anda processor operationally coupled to the transceiver. The processor isconfigured for: generating a MIMO packet including at least one spatialstream set transmitted respectively to at least one receiver, whereineach spatial stream set is encoded on the basis of one of two encodingschemes; transmitting first control information including a MIMOindicator and a first MCS field, wherein the MIMO indicator indicateswhether the MIMO packet is for SU-MIMO or MU-MIMO, and the first MCSfield indicates an MCS used for the MIMO packet if the MIMO packet isfor SU-MIMO transmission, and indicates an encoding scheme applied foreach of the spatial stream sets if the MIMO packet is for MU-MIMOtransmission; and transmitting the MIMO packet to at least one receiver.The two encoding schemes are LDPC encoding scheme and BCC encoding.

In still another aspect, a method of decoding a MIMO packet by areceiver in a WLAN system is provided. The method includes: receiving aMIMO indicator indicating whether a MIMO packet including at least onespatial stream set transmitted to at least one receiver is for MU-MIMOtransmission or for SU-MIMO transmission, wherein if the MIMO packet isfor MU-MIMO transmission, the MIMO indicator indicates MU-MIMOtransmission by indicating a receiver group of the MIMO packet;receiving a coding field, wherein the coding field indicates an encodingscheme applied to a first spatial stream set among the at least onespatial set; receiving a first MCS field, wherein the first MCS fieldindicates an MCS used for the MIMO packet if the MIMO packet is forSU-MIMO transmission, and indicates an encoding scheme applied to eachof the remaining sets other than the first spatial stream set among theat least one spatial stream set if the MIMO packet is for MU-MIMOtransmission; and receiving the MIMO packet. If the MIMO packet is forMU-MIMO, the method further include: confirming whether the receiver isa member of the receiver group; and if the receiver is the member of thereceiver group, decoding the MIMO packet according to an encoding schemeapplied to a spatial stream set of the receiver among encoding schemesindicated by the coding field and the first MCS field.

The method of claim 7, wherein if the MIMO packet is for SU-MIMO,decoding the MIMO packet according to the encoding scheme indicated bythe coding field.

Advantageous Effects

In case of transmitting and receiving a physical layer convergenceprocedure (PLCP) protocol data unit (PPDU), a transmission scheme can beconfirmed by interpreting control information included in the PPDU. Areception station (STA) can differently interpret control informationadditionally provided according to the transmission scheme, and canobtain data by performing decoding and demodulation according to asupported encoding scheme and modulation and coding scheme (MCS).

When a plurality of multi user-multiple input multiple output (MU-MIMO)paired STAs have different supported capabilities such as a supportedencoding scheme or the like, an access point (AP) that transmits a PPDUcan provide a service to a various types of STAs by providing the STAswith control information that can be interpreted differently accordingto a PPDU transmission scheme. This can improve compatibility with awireless local area network (WLAN) system.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a structure of a wireless local area network (WLAN) systemto which an embodiment of the present invention is applicable.

FIG. 2 shows a physical layer architecture of a WLAN system supported byinstitute of electrical and electronics engineers (IEEE 802.11).

FIG. 3 shows an example of a physical layer convergence procedure (PLCP)protocol data unit (PPDU) format applicable to an embodiment of thepresent invention.

FIG. 4 is a flow diagram showing an example of a PPDU transmission andreception method according to an embodiment of the present invention.

FIG. 5 is a flow diagram showing a PPDU transmission method on the basisof a multi user-multiple input multiple output (MU-MIMO) transmissionscheme according to an embodiment of the present invention.

FIG. 6 is a flow diagram showing a PPDU transmission method on the basisof a single user (SU)-MIMO transmission scheme according to anembodiment of the present invention.

FIG. 7 is a block diagram showing a wireless apparatus to which anembodiment of the present invention is applicable.

MODE FOR INVENTION

FIG. 1 is a diagram showing the configuration of a WLAN system to whichembodiments of the present invention may be applied.

Referring to FIG. 1, A WLAN system includes one or more Basic ServiceSet (BSSs). The BSS is a set of stations (STAs) which can communicatewith each other through successful synchronization. The BSS is not aconcept indicating a specific area

An infrastructure BSS includes one or more non-AP STAs STA1, STA2, STA3,STA4, and STA5, an AP (Access Point) providing distribution service, anda Distribution System (DS) connecting a plurality of APs. In theinfrastructure BSS, an AP manages the non-AP STAs of the BSS.

On the other hand, an Independent BSS (IBSS) is operated in an Ad-Hocmode. The IBSS does not have a centralized management entity forperforming a management function because it does not include an AP. Thatis, in the IBSS, non-AP STAs are managed in a distributed manner. In theIBSS, all STAs may be composed of mobile STAs. All the STAs form aself-contained network because they are not allowed to access the DS.

An STA is a certain functional medium, including Medium Access Control(MAC) and wireless-medium physical layer interface satisfying theInstitute of Electrical and Electronics Engineers (IEEE) 802.11standard. Hereinafter, the STA refers to both an AP and a non-AP STA.

A non-AP STA is an STA which is not an AP. The non-AP STA may also bereferred to as a mobile terminal, a wireless device, a wirelesstransmit/receive unit (WTRU), a user equipment (UE), a mobile station(MS), a mobile subscriber unit, or simply a user. For convenience ofexplanation, the non-AP STA will be hereinafter referred to the STA.

The AP is a functional entity for providing connection to the DS througha wireless medium for an STA associated with the AP. Althoughcommunication between STAs in an infrastructure BSS including the AP isperformed via the AP in principle, the STAs can perform directcommunication when a direct link is set up. The AP may also be referredto as a central controller, a base station (BS), a node-B, a basetransceiver system (BTS), a site controller, etc.

A plurality of infrastructure BSSs including the BSS shown in FIG. 1 canbe interconnected by the use of the DS. An extended service set (ESS) isa plurality of BSSs connected by the use of the DS. APs and/or STAsincluded in the ESS can communicate with each another. In the same ESS,an STA can move from one BSS to another BSS while performing seamlesscommunication.

In a WLAN system based on IEEE 802.11, a basic access mechanism of amedium access control (MAC) is a carrier sense multiple access withcollision avoidance (CSMA/CA) mechanism. The CSMA/CA mechanism is alsoreferred to as a distributed coordinate function (DCF) of the IEEE802.11 MAC, and basically employs a “listen before talk” accessmechanism. In this type of access mechanism, an AP and/or an STA sensesa wireless channel or medium before starting transmission. As a resultof sensing, if it is determined that the medium is in an idle status,frame transmission starts by using the medium. Otherwise, if it issensed that the medium is in an occupied status, the AP and/or the STAdoes not start its transmission but sets and waits for a delay durationfor medium access.

The CSMA/CA mechanism also includes virtual carrier sensing in additionto physical carrier sensing in which the AP and/or the STA directlysenses the medium. The virtual carrier sensing is designed to compensatefor a problem that can occur in medium access such as a hidden nodeproblem. For the virtual carrier sending, the MAC of the WLAN systemuses a network allocation vector (NAV). The NAV is a value transmittedby an AP and/or an STA, currently using the medium or having a right touse the medium, to anther AP or another STA to indicate a remaining timebefore the medium returns to an available state. Therefore, a value setto the NAV corresponds to a period reserved for the use of the medium byan AP and/or an STA transmitting a corresponding frame.

An IEEE 802.11 MAC protocol, together with a DCF, provides a HybridCoordination Function (HCF) based on a Point Coordination Function (PCF)in which a reception AP or a reception STA or both periodically poll adata frame using the DCF and a polling-based synchronous access scheme.The HCF includes Enhanced Distributed Channel Access (EDCA) in which aprovider uses an access scheme for providing a data frame to a number ofusers as a contention-based scheme and HCF Controlled Channel Access(HCCA) employing a non-contention-based channel access scheme employinga polling mechanism. The HCF includes a medium access mechanism forimproving the Quality of Service (QoS) of a WLAN and can transmit QoSdata both in a Contention Period (CP) and a Contention-Free Period(CFP).

FIG. 2 shows a physical layer architecture of a WLAN system supported byIEEE 802.11.

The IEEE 802.11 PHY architecture includes a PHY layer management entity(PLME), a physical layer convergence procedure (PLCP) sub-layer 210, anda physical medium dependent (PMD) sub-layer 200. The PLME provides a PHYmanagement function in cooperation with a MAC layer management entity(MLME). The PLCP sub-layer 210 located between a MAC sub-layer 220 andthe PMD sub-layer 200 delivers to the PMD sub-layer 200 a MAC protocoldata unit (MPDU) received from the MAC sub-layer 220 under theinstruction of the MAC layer, or delivers to the MAC sub-layer 220 aframe received from the PMD sub-layer 200. The PMD sub-layer 200 is alower layer of the PDCP sub-layer and serves to enable transmission andreception of a PHY entity between two STAs through a radio medium. TheMPDU delivered by the MAC sub-layer 220 is referred to as a physicalservice data unit (PSDU) in the PLCP sub-layer 210. Although the MPDU issimilar to the PSDU, when an aggregated MPDU (A-MPDU) in which aplurality of MPDUs are aggregated is delivered, individual MPDUs andPSDUs may be different from each other.

The PLCP sub-layer 210 attaches an additional field includinginformation required by a PHY transceiver in a process of receiving thePSDU from the MAC sub-layer 220 and delivering the PSDU to the PMDsub-layer 200. The additional field attached to the PSDU in this casemay be a PLCP preamble, a PLCP header, tail bits required to reset anconvolution encoder to a zero state, etc. The PLCP preamble serves toallow a receiver to prepare a synchronization function and antennadiversity before the PSDU is transmitted. In the PSDU, the data fieldmay include padding bits, a service field including a bit sequence forinitializing a scrambler, and a coded sequence obtained by encoding abit sequence to which tail bits are attached. In this case, eitherbinary convolutional coding (BCC) encoding or low density parity check(LDPC) encoding can be selected as an encoding scheme according to anencoding scheme supported in an STA that receives a PLCP protocol dataunit (PPDU). The PLCP header includes a field that contains informationon a PPDU to be transmitted, which will be described below in greaterdetail with reference to FIG. 3.

The PLCP sub-layer 210 generates a PPDU by attaching the aforementionedfield to the PSDU and transmits the generated PPDU to a reception STAvia the PMD sub-layer. The reception STA receives the PPDU, acquiresinformation required for data recovery from the PLCP preamble and thePLCP header, and recovers the data.

Unlike the conventional WLAN system, the next generation WLAN systemrequires a higher throughput. This is called a very high throughput(VHT). For this, the next generation WLAN system intends to support 80MHz, contiguous 160 MHz, non-contiguous 160 MHz bandwidth transmissionand/or higher bandwidth transmission. In addition, a multi user-multipleinput multiple output (MU-MIMO) transmission scheme is provided for thehigher throughput. In the next generation WLAN system, an AP cantransmit a data frame simultaneously to at least one or more MU-MIMOpaired STAs.

Referring back to FIG. 1, in the WLAN system shown in the drawing, theAP 10 can simultaneously transmit data to an STA group including atleast one STA among a plurality of STAs 21, 22, 23, 24, and 30associated with the AP 10. Data to be transmitted to each STA can betransmitted through a different spatial stream. A data packet to betransmitted by the AP 10 is a PPDU generated and transmitted in aphysical layer of the WLAN system or a data field included in a PPDU,and can be referred to as a frame. That is, the data field included inthe PPDU for SU-MIMO and/or MU-MIMO can be called a MIMO packet. It isassumed in the embodiment of the present invention that the STA1 21, theSTA2 22, the STA3 23, and the STA4 24 belong to a transmission targetSTA group which is MU-MIMO paired with the AP 10. In this case, data maynot be transmitted to a specific STA of the transmission target STAgroup since a spatial stream is not allocated to the specific STA.Meanwhile, although the STAa 30 is associated with the AP, it is assumedthat the STAa 30 is an STA not included in the transmission target STAgroup.

An identifier can be allocated to a transmission target STA group inorder to support MU-MIMO transmission in the WLAN system, and such anidentifier is called a group identifier (ID). The AP transmits a groupID management frame including group definition information for group IDallocation to STAs supporting MU-MIMO transmission. Accordingly, thegroup ID is allocated to STAs before PPDU transmission. A plurality ofgroup IDs may be allocated to one STA.

Table 1 below shows an information element included in the group IDmanagement frame.

TABLE 1 order information 1 category 2 VHT action 3 membership status 4spatial stream position

In the category field and the VHT action field, a frame corresponds to amanagement frame, and is configured to be able to identify a group IDmanagement frame used in a next generation WLAN system supportingMU-MIMO.

As shown in Table 1, the group definition information includesmembership status information indicating whether it belongs to aspecific group ID, and if it belongs to the specific group ID, includesspatial stream location information indicating at which position aspatial stream set of a corresponding STA is located among all spatialstreams based on MU-MIMO transmission.

Since one AP manages a plurality of group IDs, the membership statusinformation provided to one STA needs to indicate whether an STA belongsto each group ID managed by the AP. Therefore, the membership statusinformation can exist in an array format of sub-fields indicatingwhether it belongs to each group ID. Since the spatial stream locationinformation indicates a location for each group ID, it can exist in anarray format of sub-fields indicating a location of a spatial stream setoccupied by an STA for each group ID.

When the AP transmits a PPDU to a plurality of STAs by using a MU-MIMOtransmission scheme, the AP transmits the PPDU by inserting informationindicating a group ID into the PPDU as control information. When the STAreceives the PPDU, the STA confirms the group ID field and thus confirmswhether the STA is a member STA of a transmission target STA group. Ifit is confirmed that the STA is the member of the transmission targetSTA group, the STA can determine at which position a spatial stream setto be transmitted to the STA is located among all spatial streams. Sincethe PPDU includes information indicating the number of spatial streamsallocated to a reception STA, the STA can receive data by searching forspatial streams allocated to the STA.

In a WLAN system, STAs may support different capabilities. The STAs mayhave different channel bandwidth capabilities. The STA may be an STA notsupporting a MIMO transmission scheme, an STA supporting a single user(SU)-MIMO transmission scheme, and an STA supporting an SU/MU-MIMOtransmission scheme. In addition, a supported encoding/decoding schememay differ depending on a type of the STA. In the WLAN system, a binaryconvolution coding (BCC) scheme is an encoding scheme that must besupported, whereas a low density parity check (LDPC) scheme is a schemethat is selectively supported. Therefore, the STA may support only theBCC encoding, or may support both the BCC encoding and the LDPCencoding.

When the AP transmits a PPDU to the STA, the AP transmits the PPDU byincluding signal information for interpreting the PPDU. Examples of thecontrol information for interpreting the PPDU may include a channelbandwidth used to transmit the PPDU, information indicating atransmission target STA or STA group of the PPDU, information regardinga transmission scheme, and MCS information. When transmitting the PPDU,the AP may perform SU-MIMO transmission to one STA or may performMU-MIMO transmission to at least one STA. In case of SU-MIMOtransmission, when one encoding scheme is included as signal informationof a PPDU, the STA can decode the PPDU. On the other hand, since eachSTA may support a different encoding scheme in case of the MU-MIMOtransmission, there is a need to report an encoding scheme individuallyfor each STA. Therefore, there is a need for a MIMO packettransmission/reception method in which the AP can transmit a PPDU byincluding information regarding an encoding scheme for each STAaccording to a transmission method, and upon reception of the PPDU, theSTA can interpret the PPDU and perform decoding in accordance with awell-known encoding scheme.

FIG. 3 shows an example of a PPDU format applicable to an embodiment ofthe present invention.

Referring to FIG. 3, a PPDU 300 includes an L-STF field 310, an L-LTFfield 320, an L-SIG field 330, a VHT-SIGA field 340, a VHT-STF field350, a VHT-LTF field 360, a VHT-SIGB field 370, and a data field 380.

A PLCP sub-layer constituting a PHY converts a PSDU delivered from a MAClayer into the data field 380 by appending necessary information to thePSDU, generates the PPDU 300 by appending several fields such as theL-STF field 310, the L-LTF field 320, the L-SIG field 330, the VHT-SIGAfield 340, the VHT-STF field 350, the VHT-LTF field 360, the VHT-SIGBfield 370, or the like, and delivers the PPDU 300 to one or more STAsthrough a physical medium dependent (PMD) sub-layer constituting thePHY.

The L-STF 310 is used for frame timing acquisition, automatic gaincontrol (AGC) convergence, coarse frequency acquisition, etc.

The L-LTF field 320 is used for channel estimation for demodulation ofthe L-SIG field 330 and the VHT-SIGA field 340.

The L-SIG field 330 is used when the L-STA receives the PPDU 300 andinterprets it to acquire data.

The VHT-SIGA field 340 is a field related to common control informationrequired by STAs for receiving the PPDU, and includes controlinformation (or signal information) for interpreting the received PPDU300. The VHT-SIGA field 340 includes channel bandwidth information usedfor PPDU transmission, information indicating either SU or MU-MIMO as aPPDU transmission scheme, if the transmission scheme is MU-MIMO,information indicating a transmission target STA group of a plurality ofSTAs which are MU-MIMO paired with the AP, information regarding aspatial stream allocated to each STA included in the transmission targetSTA group, identifier information related to whether space time blockcoding (STBC) is used, information related to a short guard interval(GI) of a transmission target STA, and modulation and coding scheme(MCS) information on a channel between a transmitter and a receiver.

The information indicating the MIMO transmission scheme and theinformation indicating the transmission target STA group can beimplemented as one piece of MIMO indication information, and forexample, can be implemented as a group ID. The group ID can be set to avalue having a specific range. A specific value in the range indicatesan SU-MIMO transmission scheme, and other values can be used as anidentifier for a corresponding transmission target STA group when theMU-MIMO transmission scheme is used to transmit the PPDU 300.

The VHT-STF 350 is used to improve performance of AGC estimation in MIMOtransmission.

The VHT-LTF 360 is used when the STA estimates a MIMO channel. Since thenext generation WLAN system supports MU-MIMO, the VHT-LTF field 360 canbe configured by the number of spatial streams in which the PPDU 300 istransmitted. In addition, when full channel sounding is supported and isperformed, the number of VHT-LTFs may increase.

The VHT-SIGB field 370 includes dedicated control information requiredwhen the plurality of MIMO-paired STAs receive the PPDU 300 to acquiredata. Therefore, the STA may be designed such that the VHT-SIGB field370 is decoded only when the common control information included in theVHT-SIGB field 370 indicates that the currently received PPDU 300 istransmitted using MU-MIMO transmission. On the contrary, the STA may bedesigned such that the VHT-SIGB field 370 is not decoded when the commoncontrol information indicates that the currently received PPDU 300 isfor a single STA (including SU-MIMO).

The VHT-SIGB field 370 includes information on modulation, encoding, andrate-matching of each STA. A size of the VHT-SIGB field 370 may differaccording to the MIMO transmission method (MU-MIMO or SU-MIMO) and achannel bandwidth used for PPDU transmission.

The data field 380 includes data intended to be transmitted to the STA.The data field 380 includes a service field for initializing a scramblerand a PLCP service data unit (PSDU) to which a MAC protocol data unit(MPDU) of a MAC layer is delivered, a tail field including a bitsequence required to reset a convolution encoder to a zero state, andpadding bits for normalizing a length of the data field.

In a WLAN system including STAs which have different capabilitiesrelated to supportable encoding schemes, an AP needs to performsignaling with respect to an encoding scheme applied to a PPDU so that atransmission target STA can normally obtain data through PPDU reception.When transmitting the PPDU by using the SU-MIMO transmission scheme, theapplied encoding scheme can be included in either a VHT-SIGA field or aVHT-SIGB field including control information. However, in a MU-MIMOtransmission scheme for transmitting a PPDU to a plurality of STAs, theAP needs to provide each STA with information regarding an encodingscheme. Such a PPDU transmission and reception method can be implementedas illustrated in FIG. 4.

FIG. 4 is a flow diagram showing an example of a PPDU transmission andreception method according to an embodiment of the present invention. Itis assumed herein that, in a WLAN system having the structure of FIG. 1,an STA1 21, an STA2 22, an STA3 23, and an STA4 24 are included in aMU-MIMO transmission target STA group, the STA1 21 and the STA2 22support both BCC/LDPC encoding schemes, and the STA3 23 and the STA4 24support only the BCC encoding scheme.

Referring to FIG. 4, although not shown, an AP 10 transmits a preambleand a VHT-SIGA field to the MU-MIMO paired STAs 21, 22, 23, and 24according to the PPDU format of FIG. 3. Subsequently, the AP 10transmits a VHT-SIGB field 410 to each of the STAs 21, 22, 23, and 24(step S410). Since the VHT-SIGB field 410 is transmitted throughbeamforming, VHT-SIGB fields 411, 412, 413, and 414 are respectivelytransmitted to the STAs 21, 22, 23, and 24. Subsequently, the AP 10transmits a data field 420 to each of the STAs 21, 22, 23, and 24 (stepS420).

When the AP 10 transmits the PPDU by using the MU-MIMO transmissionscheme, the AP 10 can transmit the PPDU by including a coding sub-field410 a including encoding indication information. In this case, thecoding sub-field 410 a is a bit field, and can be set to ‘0’ when usingBCC encoding and can be set to ‘1’ when using LDPC encoding. When thecoding sub-field 410 a is included in the VHT-SIGB field 410 includingdedicated control information for each STA, the AP 10 can signalencoding information for each of a plurality of MU-MIMO paired STAs.However, as a method of indicating an encoding scheme, a bit value canbe used in an opposite way.

If coding sub-fields 411 a and 412 a included in the VHT-SIGB fields 411and 412 transmitted to the STA1 21 and the STA2 22 are set to ‘0’, theSTA1 21 and the STA2 22 obtain data by performing BCC decoding on datafields 421 and 422 transmitted to the STA1 21 and the STA2 22 inaccordance with BCC encoding, and if the coding sub-fields 411 a and 412a are set to ‘1’, the STA1 21 and the STA2 22 can obtain data byperforming LDPC decoding on the data fields 421 and 422 in accordancewith LDPC encoding. If coding sub-fields 413 a and 414 a included in theVHT-SIGB fields 413 and 414 transmitted to the STA3 23 and the STA4 24are set to ‘0’, the STA3 23 and the STA4 24 obtain data by performingBCC decoding on data fields 423 and 424 transmitted to the STA3 23 andthe STA4 24 in accordance with BCC encoding. If the coding sub-fields413 a and 414 a are set to ‘1’, this can be ignored and BCC decoding canbe performed. However, since the AP 10 can obtain information regardinga capability of an STA associated through a process of associating withthe STA, a coding sub-field value can be set such that BCC encoding isindicated for the STAs 23 and 24 supporting BCC encoding, and LDPCencoding is indicated for the STAs 21 and 22 supporting LDPC encoding.

According to the embodiment of FIG. 4, the AP 10 can indicate anencoding scheme to each STA. However, a latency problem may occur sincea data field can be decoded only after a value of the coding sub-field410 a is confirmed by interpreting the VHT-SIGB field 410. In order tosolve the latency problem, a PPDU transmission method can be proposed inwhich a coding sub-field indicating an encoding scheme in use isincluded in the VHT-SIGA field.

FIG. 5 is a flow diagram showing a PPDU transmission method on the basisof a MU-MIMO transmission scheme according to an embodiment of thepresent invention. An AP transmits a PPDU to a plurality of MU-MIMOpaired STAs.

Referring to FIG. 5, an AP 10 transmits a VHT-SIGA field 510 to an STA121, an STA2 22, an STA3 23, and an STA4. The VHT-SIGA field 510 includesa group ID sub-field 511 including a group ID as a MIMO indicator, aspatial stream sub-field 512 including information that indicates thenumber of spatial streams transmitted to an STA included in an STA groupindicated by the group ID, a coding sub-field 513 indicating an encodingscheme of an encoded PSDU included in a data field 530, and an MCSsub-field 514 indicating an MCS index of a channel between the AP 10 andthe STA or indicating an encoding scheme of a PSDU.

The group ID sub-field 511 can be set to a value indicating an STA groupincluding the STA1 21, the STA2 22, the STA3 23, and the STA4 24. Inthis case, the group ID implies that a PPDU transmitted by the AP 10corresponds to an MU-MIMO PPDU transmitted by using an MU-MIMOtransmission scheme. More specifically, the group ID can be set to avalue in the range of 0 to 63. In this case, the values 0 and 63 areused to indicate that the PPDU is transmitted by using SU-MIMO. Sincevalues 1 to 62 indicate specific STA groups, these values imply that thePPDU is transmitted by using MU-MIMO.

The spatial stream sub-field 512 indicates the number of spatial streamsallocated to the respective STAs of the STA group indicated by the groupID in the group ID sub-field 511. The spatial stream sub-field 512 canbe set such that the number of spatial streams is indicated from 0 to 4by assigning 3 bits per one STA. When the number of spatial streams is0, it implies that there is no data to be transmitted to a correspondingSTA.

When the group ID sub-field 511 is set to a value indicating thattransmission is performed using MU-MIMO, the coding sub-field 513 andthe MCS sub-field 514 are set to a value indicating an encoding schemeof a PSDU. A PPDU transmitted using MU-MIMO includes data fields 531,532, and 533 which are intended to be transmitted respectively to theplurality of STAs. Coded data sequences respectively included in thedata fields 531, 532, and 533 may use different encoding schemes. Thatis, a data sequence transmitted to an STA supporting only BCC encodingis coded by using a BCC encoding scheme, whereas a data sequencetransmitted to an STA supporting both BCC/LDPC encoding schemes can becoded by using an LDPC encoding scheme. Therefore, information regardingan encoding scheme of a coded data sequence included in a data fieldwhich is intended to be transmitted to each STA needs to be transmittedto each transmission target STA. For this, the coding sub-field 513 canbe configured to indicate an encoding scheme applied to the data field531 to be transmitted to the STAT 21, and the MCS sub-field 514 can beconfigured to indicate an encoding scheme applied to the respective datafields 532 and 533 to be transmitted to the STA2 22, the STA3 23, andthe STA4 24. The STA4 24 to which no spatial stream is allocated can beconfigured to indicate any one of encoding schemes supported by the STA424, or can be configured to indicate LDPC encoding when the LDPCencoding is supported. That is, BCC encoding can be indicated when avalue included in the coding sub-field 513 and the MCS sub-field 514 is‘0’, and LDPC encoding can be indicated when the value is ‘1’, whichimplies that an encoding scheme for each STA can be indicated in abitmap format.

The AP 10 transmits a VHT-SIGB field 520 by using a spatial streamallocated to each of STAs 21, 22, and 23 (step S520). The VHT-SIGB field520 may include information indicating a length of a PSDU to betransmitted to a transmission target STA and an MCS index informationfor a channel between the AP 10 and each of the STAs 21, 22, and 23.Subsequently, the AP 10 transmits the data fields 531, 532, and 533respectively to the STAs 21, 22, and 23 (step S530). The VHT-SIGB field520 and the data field 530 are transmitted through beamforming accordingto a MU-MIMO transmission scheme.

By using the group ID of the group ID sub-field 511 of the VHT-SIGAfield 510 transmitted from the AP 10, the STAs 21, 22, 23, and 24 canknow whether they are transmission target STAs and whether a PPDU istransmitted by using MU-MIMO. The STA1 21, the STA2 22, and the STA3 23can use the spatial stream sub-field 512 to confirm the number ofspatial streams allocated to them. When the number of spatial streams is0, the STA4 24 can know that there is no data to be transmitted to theSTA4 24. In addition, by receiving a group ID management frame beforePPDU transmission, the STAs 21, 22, 23, and 24 can know whether theybelong to a specific group ID and can know their spatial stream setlocation information regarding a specific group ID. Therefore, the STAs21, 22, 23, and 24 can receive the PPDU and can know which spatialstreams are allocated to them.

Since a PPDU is transmitted using MU-MIMO, the STA1 21, the STA2 22, andthe STA3 23 interpret the coding sub-field 513 and the MCS sub-field 514as information indicating an encoding scheme of a data field. Therefore,in accordance with an encoding scheme indicated by the coding sub-field513, the STA1 21 can obtain data by decoding the data field 531transmitted by the use of a decoding scheme corresponding to theencoding scheme and MCS index information included in the VHT-SIGB field520. The STA2 22 and the STA3 23 can obtain data by decoding thetransmitted data fields 532 and 533 in accordance with an encodingscheme indicated by the MCS sub-field 514.

In the PPDU transmission and reception method of FIG. 5, the VHT-SIGBfield 520 and the data field 530 are beam-formed and then aretransmitted to each STA through a spatial stream. Therefore, betweenVHT-SIGA field transmission (step S510) and VHT-SIGB field transmission(step S520), the AP 10 can transmit a long training field (LTF)including a training sequence for channel estimation between the AP 10and the plurality of MU-MIMO paired STAs 21, 22, 23, and 24.

Meanwhile, when the PPDU is transmitted using SU-MIMO, it is enough forthe AP to report one encoding scheme to one reception STA. This will bedescribed hereinafter in detail with reference to FIG. 6.

FIG. 6 is a flow diagram showing a PPDU transmission method on the basisof an SU-MIMO transmission scheme according to an embodiment of thepresent invention. An AP transmits a PPDU to a specific STA.

Referring to FIG. 6, an AP 10 transmits a VHT-SIGA field 610 to an STAa30 (step S610). The VHT-SIGA field 610 includes a group ID sub-field611, a spatial stream sub-field 612, a coding sub-field 613, and an MCSsub-field 614 similarly to those shown in FIG. 5. However, when a PPDUis transmitted using SU-MIMO, bit sequence values or a bit value whichis set in the aforementioned sub-field can be interpreted differentlyfrom the embodiment of FIG. 4.

The group ID sub-field 611 can be set to a value indicating that a PPDUis transmitted using an SU-MIMO transmission scheme. For example, thegroup ID sub-field 611 can be configured to indicate either 0 to 63. Byinterpreting a value of the group ID sub-field 611 included in theVHT-SIGA field, the STAa 30 can know that the PPDU is transmitted usingSU-MIMO.

The spatial stream sub-field 612 indicates the number of spatial streamsallocated to transmit the PPDU to the STAa 30. In case of MU-MIMOtransmission of FIG. 5, this field can be interpreted to indicate thenumber of spatial streams allocated to each of a plurality of STAs. Onthe other hand, in case of SU-MIMO transmission, this field isconfigured to indicate the number of spatial streams allocated to atransmission target STA, and the remaining bits can be configured toindicate a partial AID of the transmission target STA. The partial AIDcan be set to a part of a bit-stream of an AID which is identificationinformation assigned when the STAa 30 is associated with the AP 10, andcan be set to 9 least significant bits (LSBs) or 9 most significant bits(MSBs). Optionally, a new bit sequence can be set to a partial AID byusing the AID.

When the spatial stream sub-field 612 is set to a value indicatingSU-MIMO transmission, the coding sub-field 613 is set to a valueindicating an encoding scheme of a PSDU. In case of SU-MIMOtransmission, the number of the transmission target STAs is one, andthus one encoding scheme is applied when generating a PPDU. Therefore,the AP 10 configures the coding sub-field 613 to indicate BCC encodingor LDPC encoding.

When the PPDU is transmitted using SU-MIMO, one piece of MCS indexinformation is enough for a channel between the AP 10 and the STAa 30.Therefore, the MCS index information is transmitted by being included inthe MCS sub-field 614 of the VHT-SIGA field 610 instead of a VHT-SIGBfield 620.

The AP 10 transmits the VHT-SIGB field 620 to the STAa 30 (step S620),and transmits a data field (step S630). The VHT-SIGB field may includeinformation indicating a length of a PSDU included in the data field tobe transmitted to the STAa 30.

By using a value which is set to the group ID sub-field 611 of theVHT-SIGA field 610 transmitted from the AP 10, the STAa 30 can know thatthe PPDU is transmitted using not MU-MIMO but SU-MIMO. In this case, theSTAa 30 can know that the spatial stream sub-field 612 includesinformation indicating the number of spatial streams allocated to theSTAa 30 and information indicating a partial AID instead of informationindicating the number of spatial streams allocated to each of theplurality of STAs, and thus can interpret a bit sequence.

The STAa 30 can know an encoding scheme applied to the data field fromthe MCS sub-field 614 and MCS index information from the codingsub-field 613, and by using this information, can obtain data byperforming decoding and demodulation on the data field.

As shown in FIG. 5 and FIG. 6, a reception STA (or a plurality ofreception STAs) of a PPDU can confirm whether a transmission scheme isMU-MIMO or SU-MIMO by using the group ID of the VHT-SIGA field 510 or610, and thereafter can obtain data by differently interpreting valueswhich are set in subsequent sub-fields.

Table 2 below shows an example of a VHT-SIGA field format indicatinginformation included in a VHT-SIGA field applied to an embodiment of thepresent invention. The VHT-SIGA field can be divided into a VHT-SIGA1field and a VHT-SIGA2 field. The VHT-SIGA1 field and the VHT-SIGA2 canbe transmitted through respective OFDM symbols. Table 2 below maycorrespond to an example of a VHT-SIGA field included in the PPDU formatof FIG. 3 applicable to the embodiment of the present invention.

TABLE 2 Bit Bit Field assignment Descriptions VHT-SIG-A1 B0-B1 Bandwidth2 0: 20 MHz, 1: 40 MHz, 2: 80 MHz, 3: 160 MHz and 80 + 80 MHz B2Reserved 1 Reserved for bandwidth expansion B3 STBC 1 Set to 1 if STBCcoding is applied to all streams, and otherwise set to 0 B4-B9 Group ID6 SU-MIMO: ‘0’ or ‘63’ MU-MIMO: Set to a value assigned to an STA groupB10-B21 Spatial stream 12 MU-MIMO: Support 3 bits per STA, maximum 4STAs (STA u uses bits B(10 + 3*u) − B(12 + 3*u) , where u = 0, 1, 2, 3)0: 0 spatial stream 1: 1 spatial stream 2: 2 spatial streams 3: 3spatial streams 4: 4 spatial streams SU-MIMO B10-B12 0: 1 spatial stream1: 2 spatial streams 2: 3 spatial streams 3: 4 spatial streams 4: 5spatial streams 5: 6 spatial streams 6: 7 spatial streams 7: 8 spatialstreams B13-B21 Partial AID: LSB bits of AID B22-B23 Reserved 2 All onesVHT-SIG-A2 B0-B1 Short GI 2 B0: 0: Short GI is not used in a data field1: Short GI is used in a data field B1: 1: If short GI is used, and thenumber of transmission symbols (Nsym) mod 1 = 9 0: otherwise B2-B3Coding 2 SU-MIMO: B2: 0: BCC encoding, 1: LDPC encoding B3: Indicate anextended OFDM symbol for an LDPC encoded packet MU-MIMO B2: Regarding1^(st) STA, 0: BCC encoding, 1: LDPC encoding B3: Indicate an extendedOFDM symbol for an LDPC encoded packet B4-B7 MCS 4 SU-MIMO B4-B7: MCSindex MU-MIMO(when the number of spatial streams for a corresponding STAis 0, each bit is set to 1) B4: Regarding 2^(nd) ST, 0: BCC encoding, 1:LDPC encoding B5: Regarding 3^(rd) STA, 0: BCC encoding, 1: LDPCencoding B6: Regarding 4^(th) STA, 0: BCC encoding, 1: LDPC encoding B7:Reserved and set to 1 B8 Beamforming 1 SU-MIMO: 1: if a beamformingsteering matrix is applied to a waveform of SU transmission: otherwiseMU-MIMO: Reserved (set to 1) B9 Reserved 1 Reserved (set to 1) B10-B17CRC 8 B18-B23 Tail 6

In addition to the PPDU transmission and reception method of FIG. 5 andFIG. 6 in which a coding sub-field indicating an applied encoding schemeis included in a VHT-SIGA field, a bit sub-field indicating an encodingscheme can be included in the VHT-SIGA field. A one-bit sized codingsub-field can be included in the VHT-SIGA field in such a manner thatBCC encoding is indicated when the field is set to ‘0’ and LDPC encodingis indicated when the field is set to ‘1’.

When all of MU-MIMO paired STAs support BCC encoding, the AP cantransmit a PPDU by setting a coding sub-field value of the VHT-SIGAfield to ‘0’. In this case, each PSDU of the transmitted data field istransmitted through BCC encoding. When all of the MU-MIMO paired STAssupport BCC and LDPC encoding, the AP can transmit the PPDU by setting acoding sub-field value of the VHT-SIGA field to ‘1’. In this case, eachPSDU of the transmitted data field is transmitted through LDPC encoding.

When some of the MU-MIMO paired STAs support BCC encoding and some ofthe MU-MIMO paired STAs support both BCC/LDPC encoding, the AP cantransmit the PPDU by setting the coding sub-field of the VHT-SIGA fieldto ‘1’. However, the AP transmits the PSDU of the data field byperforming encoding according to a corresponding encoding scheme inaccordance with an encoding scheme that can be supported by atransmission target STA. In this case, the STAs supporting both BCC/LDPCencoding can decode the data field in accordance with LDPC encoding.However, the STAs supporting only BCC encoding can decode the data fieldin accordance with BCC encoding while ignoring a value of the codingsub-field.

According to the PPDU transmission method described above with referenceto the drawings, the AP can transmit PPDUs each using a differentencoding scheme with respect to STAs supporting different encodingschemes through a MU-MIMO transmission scheme, and MU-MIMO paired STAscan confirm an appropriate decoding scheme and then can obtain data byperforming decoding.

FIG. 7 is a block diagram showing a wireless apparatus to which anembodiment of the present invention is applicable. The wirelessapparatus may be an AP or an STA.

A wireless apparatus 700 includes a processor 710, a memory 720, and atransceiver 730. The transceiver 730 transmits and/or receives a radiosignal, and implements an IEEE 802.11 PHY layer. The processor 710 isoperationally coupled to the transceiver 730, and implements IEEE 802.11MAC and PHY layers. The processor 710 can be configured to generate aPPDU format proposed in the present invention and to transmit the PPDUformat. Further, the processor 710 can be configured to acquire controlinformation by receiving the transmitted PPDU and interpreting a fieldvalue included in the PPDU and to acquire data by using the controlinformation. The processor 710 can be configured to implement theaforementioned embodiment of the present invention described withreference to FIG. 2 to FIG. 6.

The processor 710 and/or the transceiver 730 may include anapplication-specific integrated circuit (ASIC), a separate chipset, alogic circuit, and/or a data processing unit. The memory 720 may includea read-only memory (ROM), a random access memory (RAM), a flash memory,a memory card, a storage medium, and/or other equivalent storagedevices. When the embodiment of the present invention is implemented insoftware, the aforementioned methods can be implemented with a module(i.e., process, function, etc.) for performing the aforementionedfunctions. The module may be stored in the memory 720 and may beperformed by the processor 710. The memory 720 may be located inside oroutside the processor 710, and may be coupled to the processor 710 byusing various well-known means.

Although the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

The invention claimed is:
 1. A method of transmitting a multiple inputmultiple output (MIMO) packet in a wireless local area network system,the method performed by a transmitting station and comprising:generating a MIMO packet including at least one spatial stream and firstcontrol information; and transmitting the MIMO packet to at least onereceiving station, wherein the MIMO packet is transmitted to a singlereceiving station if the MIMO packet is generated based on a single user(SU)-MIMO scheme, and the MIMO packet is transmitted to a plurality ofreceiving stations if the MIMO packet is generated based on a multi user(MU)-MIMO scheme, wherein the first control information includes a firstfield indicating a group ID of the at least one receiving station andfurther indicating whether the MIMO packet is generated based on theSU-MIMO scheme or the MU-MIMO scheme, wherein the first controlinformation includes a second field, and wherein content of the secondfield is determined based on whether the MIMO packet is generated basedon the SU-MIMO scheme or the MU-MIMO scheme, the second field indicatesa modulation and coding scheme (MCS) index used for the MIMO packet ifthe MIMO packet is generated based on the SU-MIMO scheme, and the secondfield indicates an encoding scheme applied to the at least one receivingstation if the MIMO packet is generated based on the MU-MIMO scheme. 2.The method of claim 1, wherein the encoding scheme comprises one of: abinary convolution coding (BCC) encoding scheme, and a low densityparity check (LDPC) encoding scheme.
 3. The method of claim 1, whereinthe MIMO packet further comprises: second control information includinga second MCS field, the second MCS field indicating an MCS index usedfor the each spatial stream set if the MIMO packet is generated based onthe MU-MIMO scheme.
 4. The method of claim 3, wherein the MIMO packetfurther comprises: a training sequence used to estimate a MIMO channelbetween the transmitting station and the at least one receiving station,and wherein the training sequence is positioned in the MIMO packetbetween the first and second control information.
 5. The method of claim1, wherein the first control information further includes a fourth fieldindicating a number of spatial streams included in the at least onespatial stream.
 6. A transmitting station configured to transmit amultiple input multiple output (MIMO) packet in a wireless local areanetwork system, comprising: a transmitter; and a controller operativelyconnected to the transmitter and configured to: generate a MIMO packetincluding at least one spatial stream and first control information, andtransmit the MIMO packet to at least one receiving station, wherein theMIMO packet is transmitted to a single receiving station if the MIMOpacket is generated based on a single user (SU)-MIMO scheme, and theMIMO packet is transmitted to a plurality of receiving stations if theMIMO packet is generated based on a multi user (MU)-MIMO scheme, whereinthe first control information is commonly received by the plurality ofreceiving station if the MIMO packet is transmitted to the plurality ofreceiving station, wherein the first control information includes afirst field indicating a group ID of the at least one receiving stationand further indicating whether the MIMO packet is generated based on theSU-MIMO scheme or the MU-MIMO scheme, and wherein the first controlinformation includes a second field that includes: a modulation andcoding scheme (MCS) index used for the MIMO packet if the MIMO packet isgenerated based on the SU-MIMO scheme, and an encoding scheme applied toeach of the plurality of receiving stations if the MIMO packet isgenerated based on the MU-MIMO scheme.
 7. The transmitting station ofclaim 6, wherein the encoding scheme comprises one of: a binaryconvolution coding (BCC) encoding scheme, and a low density parity check(LDPC) encoding scheme.
 8. The transmitting station of claim 6, whereinthe MIMO packet further comprises: second control information includinga second MCS field, the second MCS field indicating an MCS index usedfor the each spatial stream set if the MIMO packet is generated based onthe MU-MIMO scheme.
 9. The transmitting station of claim 8, wherein theMIMO packet further comprises: a training sequence used to estimate aMIMO channel between the transmitting station and the at least onereceiving station, and wherein the training sequence is positioned inthe MIMO packet between the first and second control information. 10.The transmitting station of claim 6, wherein the first controlinformation further includes a fourth field indicating a number ofspatial streams included in the at least one spatial stream.
 11. Amethod of receiving a multiple input multiple output (MIMO) packet in awireless local area network system, the method performed by a receiverand comprising: receiving a MIMO packet from a transmitting station, theMIMO packet including at least one spatial stream and first controlinformation; and processing the received MIMO packet, wherein the MIMOpacket is generated for a single receiving station if the MIMO packet isgenerated based on a single user (SU)-MIMO scheme, and the MIMO packetis generated for a plurality of receiving stations if the MIMO packet isgenerated based on a multi user (MU)-MIMO scheme, wherein the firstcontrol information includes a first field that indicates whether theMIMO packet is generated based on the SU-MIMO scheme or the MU-MIMOscheme, and wherein the first control information includes a secondfield that includes: a modulation and coding scheme (MCS) index used forthe MIMO packet if the MIMO packet is generated based on the SU-MIMOscheme, and an encoding scheme to be used by the receiving station ifthe MIMO packet is generated based on the MU-MIMO scheme.
 12. The methodof claim 11, wherein the encoding scheme comprises one of: a binaryconvolution coding (BCC) encoding scheme, and a low density parity check(LDPC) encoding scheme.
 13. The method of claim 11, wherein the MIMOpacket further comprises: second control information including a secondMCS field, the second MCS field indicating a MCS used for the eachspatial stream set if the MIMO packet is generated base on the MU-MIMOscheme.
 14. The method of claim 13, wherein the MIMO packet furthercomprises: a training sequence used to estimate a MIMO channel betweenthe transmitting station and the receiving station, and wherein thetraining sequence is positioned in the MIMO packet between the first andsecond control information.
 15. The method of claim 11, wherein thefirst control information further includes a fourth field indicating anumber of spatial streams included in the at least one spatial stream.16. A receiving station configured to receive a multiple input multipleoutput (MIMO) packet in a wireless local area network system,comprising: a receiver; and a controller operatively connected to thereceiver and configured to: receive a MIMO packet from a transmittingstation, the MIMO packet including at least one spatial stream and firstcontrol information, and process the received MIMO packet, wherein theMIMO packet is generated for a single receiving station if the MIMOpacket is generated based on a single user (SU)-MIMO scheme, and theMIMO packet is generated for a plurality of receiving stations if theMIMO packet is generated based on a multi user (MU)-MIMO scheme, whereinthe first control information includes a first field that indicateswhether the MIMO packet is generated based on the SU-MIMO scheme or theMU-MIMO scheme, wherein the first control information includes a secondfield, and wherein content of the second field is determined based onwhether the MIMO packet is generated based on the SU-MIMO scheme or theMU-MIMO scheme, the second field indicates a modulation and codingscheme (MCS) index used for the MIMO packet if the MIMO packet isgenerated based on the SU-MIMO scheme, and the second field indicates anencoding scheme applied to the at least one receiving station if theMIMO packet is generated based on the MU-MIMO scheme.
 17. The receivingstation of claim 16, wherein the encoding scheme comprises one of: abinary convolution coding (BCC) encoding scheme, and a low densityparity check (LDPC) encoding scheme.
 18. The receiving station of claim16, wherein the MIMO packet further comprises: second controlinformation including a second MCS field, the second MCS fieldindicating an MCS index used for the each spatial stream set if the MIMOpacket is generated base on the MU-MIMO scheme.
 19. The receivingstation of claim 18, wherein the MIMO packet further comprises: atraining sequence used to estimate a MIMO channel between thetransmitting station and the receiving station, and wherein the trainingsequence is positioned in the MIMO packet between the first and secondcontrol information.
 20. The receiving station of claim 16, wherein thefirst control information further includes a fourth field indicating anumber of spatial streams included in the at least one spatial stream.